Final detailingpp

Design of RCC structures
Detailing of Reinforcement
(IS456-2000, IS13920)
Pradip Paudel
(M.Sc. in Structural Engineering)

WHO IS AN ENGINEER?
 The great liability of the engineer …compared
to men of other professions……is that his
works are out in the open where all can see
them.
 He cannot bury his mistakes in the grave like
the DOCTORS.
 He cannot, like the ARCHITECT, cover his
figures with trees
 A design engineer’s responsibility should
include assuring the structural safety of the
design, details, checking shop drawing.
 Detailing is as important as design

Requirements of Good Detailing
 Should be simple for fabrication and placing
 Check spacing for crack control – maximum spacing
 Minimum spacing for concrete placing
 Check for splicing requirements and development
length
 Special care for section of varying depth and sloped
slabs
 Care for corner joints, beam column junction,
openings etc.

 Detailing for gravity loads is different from
the lateral loads specially for the SEISMIC
FORCES.
 Apart from the detailing for the above there
is a different detailing required for the
rehabilitation and strengthening of damaged
structures.
 Detailing codes SP16 and IS456-2000
 EQ code is 13920 as required for seismic
forces.
Cont.…

Minimum Nominal Cover
Clear cover shall be provided
 To develop the desired bond strength through out the
perimeter of steel
 To protect against corrosion and fire
 Slab 20mm
 Beam 25mm
 Column 40mm
 Footing 60mm
For detail see Table-16 IS 456-2000

Spacing of reinforcement
The horizontal distance between two parallel main
reinforcing bars shall not be less than
 The diameter of the bar if the bars are of equal
diameter
 The diameter of the larger bar
 5mm + nominal size of aggregate
 Maximum spacing ----as per design
 Further reading Page 167 A. K. Jain
Clause 26.3.2, IS456-2000

Limits for reinforcement
 Beam
 Min As/bd = 0.85/Fy
 Maximum = 4% of bD
 Compression = 0.2%
 Web reinforcement = 0.1% of web area
 Vertical Shear bars not exceeding 0.75d or
300mm whichever is less.
 Minimum shear bars = cl 26.5.1.6
 Slab = min 0.12% for Fe415 and 0.15% for
Fe250
Clause 26.5, IS456-2000

 The stirrups shall be minimum size of 8mm
in the case of lateral load resistance .
 The hooks shall be bent to 135 degree .
 In column size of bar not less than 12 mm
 Spacing of bars not greater than 300mm
 Arrangement of lateral ties as per cl 26.5.3.2

DEVELOPMENT LENGTH OF BARS
SLNO BAR DIA. TENSIONm
m
COMPRESSION REMARKS
1 8 376.0 301.0
2 10 470.0 376.0
3 12 564.0 451.0
4 16 752.0 602.0
5 20 940.0 752.0
6 22 1034.0 827.0
7 25 1175.0 940.0
8 28 1316.0 1053.0
9 32 1504.0 1203.0
FOR A CONCRETE GRADE M20 &STEEL
STRENGTH Fy=415
APPROXIMATELY USE 50Xdia FOR TENSION

 Lap splicing -clause 26.2.5.1 IS456-2000

Lap splicing as per clause 26.2.5.1 IS456-2000
 Lap splices should not be used for bar larger than
36mm
 Larger than 36mm bar may be welded
 Lap length including anchorage value of hooks in
flexural tension is development length (Ld)or 30ϕ
whichever is greater.
 Lap length including anchorage value of hooks in
direct tension is 2Ld or 30ϕ whichever is greater.
 The straight lap length should not be less than
200mm or 15ϕ whichever is greater.

Lap splicing Cont.….
 Lap splices are considered as staggered if the c/c
distance of the splices is not less than 1.3 times the
lap length.
 The lap length in compression is equal to the
development length in compression but not less
than 24ϕ.
 Lap length is calculated on the basis of diameter of
smaller bar when bars of different diameters are to
be spliced.

DO’S For Detailing
 Prepare drawing properly and accurately
 Prepare bar bending schedule, if necessary
 Indicate proper cover to the reinforcement
 Decide location of the openings/hole and
supply adequate details for the
reinforcement around openings.
 Commonly available size of bars and spirals
shall be used for reinforcement.

 For a single structural member the number of different
sizes of reinforcement bar should be minimum.
 The grade of reinforcement bars should be clearly
mention in the structural drawings
 When reinforcement is left exposed for future
construction, it should be adequately protected from
corrosion and weathering.
 Congestion of the reinforcement should be avoided at
points where members intersect and make certain that
all the reinforcement shown can be properly placed.
 Show enlarged details at the corners, beam and
column joint and at similar special situations.

Do Not's for Detailing
 Flexure reinforcement shall not be
terminated in a tension zone.
 Lap splices should not be used for bars
larger than 36 mm dia.
 Different types of reinforcing bars such as
deformed bars and plain bars and various
grades should not be used side by side as
this practice would lead to confusion at site.

Do’s for Columns
 A reinforced column should have min 4
bars for rectangular or square column and
minimum 6 bars for circular columns.
 Keep outer dimensions of the column
constant, as far as possible, for re-use of
forms.
 Preferably avoid use of two grades of
vertical bars in the same element.

Do’s for Beams and Slabs
 Where splices are provided in the reinforcing
bars, they should be staggered, and away
from the sections of maximum stress.
 Where the depth of the beam exceeds 750
mm in case of beams without torsion and 450
mm with torsion side face reinforcement
shall be provided.
 All spacing shall be c/c spacing of the bars.

 Deflection in beams/slabs may be reduced by
providing compression reinforcement.
 At beam column intersection ,ensure that the
main beam bars avoid the main column bars.
 At beam column intersections , main
reinforcement may be so arranged that layers
in mutually perpendicular beams are at
different levels.
 To accommodate bottom bars, it is good
practice to make secondary beams shallower
than the main beams at least by 50 mm.

Curtailment of reinforcement
Clause26.2.3 IS456

 Positive moment reinforcement, Cl26.2.3.3
 Negative moment reinforcement,Cl26.2.3.4
 Curtailment of bundled bars,Cl26.2.3.5
 Further reading A. K. Jain p 172
Simplified rules of curtailment as per BS
8110-1985
Cont.…

Bar Bending Schedule
Bar Bending Schedule should include:
 Identification of structural member
 Position of each bar in the member
 Bar marks and diameter of each bar
 Number of bars
 Shape and bending dimension of each bar
 Length of each bar
 Remark, if any
Typical example for slab, beam and column: see page 180 (A.K.
Jain)

IS13920:1993,Ductile Detailing of
RCC Structures Subjected to Seismic Forces
 This code applies to all RCC
structures which satisfy one of the
four conditions-
 The structure is located –
 In zone IV or V
 In zone III and I> 1.0
 In zone III and industrial structure
 In zone III and is more than 5 story high

What is EQ Resistant Design?
 The acceptable response levels of the
structure under design earthquake.
 Designer should exercise some degree
of control on magnitude and
distribution of stiffness, mass and
relative strength of member and their
ductility to achieved desired results.

Seismic Design Criteria(IS 1893)
Earthquake Desired Behavior Controlling parameters
Minor No damage to non-
structural components
Control deflection by
providing stiffness
Moderate No significant structural
damage, minor cracks in
beam and columns,
Response should be
predominantly elastic
Avoid yielding of
members or permanent
damage by providing
strength
Severe,
Catastrophic
No collapse of the system
which could cause loss of
life.
Allow structure to enter
into inelastic range and
absorb energy by
providing ductility

 If elastic strength of structural elements
exceeds the greatest imposed load upon that
structure there can be no significant damage.
 In severe earthquake some of the resisting
elements will be loaded to their full
strength. If they are brittle, they will fail,
throwing their share of the load on the
remaining elements. If they are ductile, they
can continue to participate in resisting the
lateral force up to their full strength after
they yield.

DUCTILITY
 A ductile material is the one that can
undergo large strains while resisting
loads
 Ductility implies the ability to sustain
significant inelastic deformations prior
to collapse.
 Brittle material is one that fails
suddenly upon attaining its maximum
load

Brittle and Ductile force-deformation behavior
Brittle
Ductile
Force
Δy Δu
Deformation

Significance of Ductility
 It can be expected to adapt to unexpected
overloads, impact and structural movements
due to foundation settlements and volume
changes.
 Occupants will have sufficient warning of the
impending failure thus reducing the probability
of loss of life in the events of collapse.
 All joints and splices must be able to withstand
forces and deformations corresponding to
yielding of the reinforcement.

Design for Ductility
 Structural layout should be simple
and regular.
 Amount of tension reinforcement
in beams should be restricted and
more compression reinforcement
should be provided.

 The shear reinforcement should be
adequate to ensure that the strength in
shear exceeds the strength in flexure and
thus, prevent a non-ductile shear failure
before the fully reversible flexural
strength of a member has been developed.
 See on clause 6.3.3 in IS13920
Cont.…

BEAMS
 At least two bars should be provided
continuously both at top and bottom.
 The positive moment resistance at the face of
the joint should not be less than one –half of the
negative moment resistance provided at that
face of the joint.
 Neither the negative nor the positive resistance
at any section along the member length should
be less than one-fourth of the moment resistance
provided at the face of the either joint
Clause 6, IS13920

HOOP SPACING
HOOP SPACING
< d/4 and 8 db
B = BREADTH OF BEAM
db = DIAMETER OF LONGITUDINAL BAR
2d
d
2d
db
50 mm max 50 mm max
MIN 2 BARS FOR FULL LENGTH
ALONG TOP AND BOTTOM FACE
AS > MIN. Bd
AS < MAX Bd
> d /2
BEAM REINFORCEMENT

 Spacing of hoops over a length of 2d at
either end of the beam shall not exceed-
 d/4
 8 times the diameter of the smallest
longitudinal bar, need not be less than
100 mm
 Elsewhere, the beam shall have vertical
hoops at a spacing not exceeding d/2.
Clause 6.3.5, IS13920

Cont.…
 The special confining reinforcement shall be
provided above and below the beam connections,
in a length of the column at each end which is
largest of the following-
 1/6 of the clear height of the column
 Larger dimension of the column
 450 mm
 When a column terminates into a footing, special
confining reinforcement shall extend at least 300
mm into the footing

SPECIAL CONFINING
REINFORCEMENT
> 300 mm
PROVISION OF SPECIAL CONFINING REINFORCEMENT IN
FOOTINGS

JOINT REINFORCEMENT
AS PER 8.1
TRANSVERSE
REINFORCEMENT
AS PER 7.2.1
CONFINED JOINT WITH BEAMS
FRAMING INTO ALL FOUR SIDES
CONFINING REINFORCEMENT AS
PER 8.2
hC
lO
> hc / 4
lO
lO
> hc / 4
COLUMN AND JOINT DETAILING

 The spacing of hoops used as special
confining reinforcement shall not
exceed –
 ¼ of the minimum member dimension
 need not be less than 75 mm nor more
than 100 mm
 For further information see on Clause
7.4.6 and 7.4.7 in IS 13920

db
Ld = DEVELOPMENT
LENGTH IN TENSION
Db = BAR DIAMETER
FIG. 1: ANCHORAGE OF BEAM BARS IN
AN EXTERNAL JOINT.

LAP SPLICES IN BEAM
 Not more than 50 % of the bars shall be spliced at
one section
 The longitudinal bars shall be spliced , only if hoops
are provided over the entire splice length, at a
spacing not exceeding 150 mm
 The lap length shall not be less than the bar
development length in tension.
Clause 6.2.6 IS13920

Cont.…
 Lap splices shall not be provided-
 within a distance of 2d from the joint face
 within a joint
 within a quarter length of the member
where flexural yielding may generally occur
under the effect of earthquake forces.
 Use of welded splices and mechanical
connections may also be made as per IS456-
1978
Clause 6.2.6 IS13920

Ld = DEVELOPMENT
LENGTH IN TENSION
db = BAR DIAMETER
db
Ld
150 mm
FIG. 2: LAP, SPLICE IN BEAM

Web Reinforcement

Clause 6.3 IS13920

Ld/2Ld/2
Ld
crack
INCORRECT
CORRECT
CLOSE
STIRRUPS
Ldt
Ldt/2
CANTILEVER BEAM

NON PRISMATIC BEAM
Ld/2 Ld/2
Ld
INCORRECT
CORRECT
CLOSE
STIRRUPS
crack
Ldt/2
Ldt

GRID BEAM
INCORRECT
1.5d1.5d1.5d
Close rings
Hanger
barsSlope 1:10
2#extra bars
300
300
d
CORRECT

Details of Main & Secondary beams
INCORRECT
1.5d1.5d1.5d
Close rings
Hanger
bars
300
300
d
CORRECT
Secondary
beam
Main
beam
Secondary beam
60degree
Main
beam

d
1/4OR
1/5 SPAN
1.5d
CORRECT
INCORRE
CT
d/2+d/2Cot(t)
t
t
Ld
d/2
d/2
Ld
LINE OF CRACK
BEAM

 Continuous Beam Span/4
Span/4
Span/4
Span/4
incorrect
Span/4
Span/4
1.5d
1.5d
Span/4
correct
1.5d

100%
L1
100% CRACK
CRACK
.08L2
.08L1
L2
SPAN/4 SPAN/4
CONTINUOUS BEAM
INCORREC
T
.08L1
.08L1
SPAN/4
CRACK
100%
L1
100%
.15L2 L2
L1/4 L2/4
CORRECT
0.1L1
.15L1
L1/4
100%
20%
20%

D
D
CRACK
INCORRE
CT
NONPRISMATIC
SECTION OF
BEAM
D
D
D
CORREC
T
D
CLOSE RING
CLOSE RING

COLU
MNINCORRE
CT
CANTILEVER BEAM
PROJECTING FROM
COLUMN
CORREC
NOT LESS THAN GREATER OF 0.5L OR Ld
50mm
0.25Ast
NOT
LESS
THAN
0.5Ast
COLU
MN
Ld
Ld/3

CRAC
K
SLOPING BEAM
CORRE
CT
Ld
Ld

CRACK
CRACK
INCORRE
CT
HAUNCH BEAMS
CORRECT
L/8 TO
L/10 L/8 TO
L/10
L
L
Ld Ld
Ld Ld

STRESSES AT CORNERS
C
C-COMPRESSION
T-TENSIONt
t
C
RESULTANT TENSILE STRESS FOR
ACROSS CORNER(ONE PLANE)
t
c
RESULTANT TENSILE STRESS FOR
ACROSS CORNER(DIFFERENT PLANE)t
c
CRACK
CRACK

SHEAR AND TORSION REIN. IN BEAMS
INCORRE
CT
Min 0.2%bd to control
deflection as well as for
seismic requ.
b
D
100 to
200mm
d
D-n>500mm
D/
5
Skin rein.10dia is
required when
depth exceeds
450mm(0.1% of
web area
distributed
equally on two
Stirrups taken round
outermost bars
spacing<=x1
<=(x1+y1)/4
<=300mm
x1
y1
D-n>500mm
n
CORREC
T

CANTILEVER BEAM WITH POINT LOAD
CORRECT
INCORRE
CT
2/3
dd
Shear
rein.
Extra ties
L
d
L
d

openi
ng
CORRECT
OPENING IN WEB OF
BEAM
crackcrack
openi
ng
INCORREC
T
OPENING IN WEB OF
BEAM
Ld
d/
2
d/
2
Closed
stps for
d/2
Closed
stps for
d/2

BEAM COLUMN JUNCTION-EXTERIOR COLUMN
CORRECT
INCORRE
CT CLOSED STPS2”max
IN TENSION-Ld
U TYPE BARS
Ld

CORRECT
SPLICE DETAIL FOR
COLUMN
INCORREC
T
COVER
CLOSE
TIES
@S/2
S-SPACING
SLOPE 1:6

REDUCTION
COLUMN
BOTH SIDES
INCORRE
CT
CORREC
3NO.CLOSE TIES
SPLICE
CLOSE STPS SPACIN
<=75mm
SLOPE 1:8 FROM
BEAM BOTTOM
3NO.CLOSE TIES

TERMINATION OF COLUMN BARS INSIDE BEAM
INCORRECT
CORRECT
Ld

BEAM COL. JUNCTION-EQ
REGION
EQ REGION-BEAM-COL JN-EXTERIOR
CORREC
T
BEAM COL. JUNCTION-EQ
REGION
INCORRE
CT
END REGION
END REGION
COL.
CORE*
SPACING OF
LATERAL
TIES
<=100mm
SPACING OF
LATERAL
TIES <=d/2
SPACING OF
LATERAL
TIES <=d/2
SPACING OF
LATERAL
TIES <=d/2
*COL.CORE HAS TO
BE CONFINED BY
CIRCULAR OR
RECTANGULAR TIES
IN ACCORDANCE
WITH END REGION

COLUMN
DETAILS
IN EQ
REGIONS
END
REGION
END
REGION
First stirrups
50mm from
beam face
Spacing of shear
rein. In columns
incorrect
Spacing of shear
correct
END REGION-h/6 or D or
450MM whichever is
greater
END
REGION
h
d
D
b

EQ-REGION-CONTINUOUS
BEAM
INCORREC
T
Ld
A=L1/3
CONTINUOUS BARS NOT LESS THAN ¼
AREA OF BARS AT COL.FACE
A=L1/3 A=L1/3
2d
50mmmax
Stirrup spacing=d/4 or
100mm or 8dia which
ever is the least
2d2d 2dstp@maxd/2 stp@maxd/2
CORRECT

INCORREC
T
FOOTING-DETAILS(INDEPENDENT)
CORRECT
COVER TO
STARTER
STARTER
BARS
COLUMN
BARS
NATURAL
G.L
Ldt
Lb
3” SIDE COVER
Ldt
COVER50mm
IF p.c.c below
or 75mm
Min.300

SECTION OF TRENCH
CRACK
INCORREC
T
INCORREC
T
CORRECT
Ld
Ld
Ld

STAIRCASE-WITH WAIST SLAB
INCORRECT
CORRECT
Ld(mi
n)
Extra
bar
Ld(mi
n)
Ld(mi
n)

Main bar
Dist.
Main bar
Alternat
e 1
SLABLESS STAIRCASE

Main bar
Alternat
e 2A=0.25L
L=horizontal
span
SLABLESS
STAIRCASE

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